Tension control system



Nol 12 1940 A G. P. LEssMANN- 2,221,592

TENSION coNTRoL'sYsTEM Filed March 27, 1937 2 sheets-sheet l bnn-allez- Golm-aller /2 ZILTL Canti-aller 23 WITNESSES: INVENTOR Gek/60rd P Lessmcmfz Nov. l2, 1940. G. F. Lr-:ssMANN 2,221,592

TENSION CONTROL SYSTEM IP11901 March 27, 1937 2 sheets-sheet 2 lNvl-:NToR

Gerhard/Z? Less/Warm.

'Patented Nov. 12, 1940 i UNITED STATES TENSION CONTROL SYSTEM Gerhard P. Lessmann. Forest Hills, Pm, asslgnor to Westinghouse Electric & Manufacturing Company, East Pittsb Pennsylvania urgh, Pa., a colllration of Application March 27, 1937, Serial No. 133.418

21 Claims.

My invention relates, generally, to tension control systems and, more particularly, to uidpressure operated tensiometers for automatically maintaining a predetermined tension on the mao terial being worked upon or handled by a plurality of work devices, such, for example, as between the rolls of a tandem or continuous mill. Numerous methods have been proposed for maintaining a predetermined constant tension lo on the material extending between the rolls of a tandem mill. One prior method is to attempt to control the tension on the material by causing the motors driving the roll stands to assume a load somewhat greater than that required to l actually reduce the material as it is passed through the rolls, the excess load being the tension load. 'I'his method has been found to be inadequate because of the diiiculty of determining and controlling the amount of tension thatis being applied, since the amount of power required tor working the material may vary from time to time, thereby causing the tension to vary and it is dimcult, if -not impossible,to determine what lpercentage of the total motor load is being used to produce tension. Another method, previously utilized, is to subject the material to a tension .by means of an idler roller mehanismlisposedto applya force transverse to the' path of movement of the material which varies in accordance withthe degree of deiiection of the material between predetermined limits of movement. Compensation for variation in the degree of deection of the material from its normal path of travel is provided by mounting the idler roller on a bell crank device having an angle between its arms which causes the tensioning device to be self-compensating over a certain range oi operation and permits a limited amount of movement of the idler roller, result- 4o ing from variations in the length of material between roll stands, without appreciably changing the tension on the material. However, the

range of operation over' which devices of this character are self-compensating is relatively small and their application is limited to rolling mills in which the position of the idler roller does not vary over a wide range.

Therefore, an object of my invention, generally stated. is to provide a means for controlling and maintaining tension on tanslatory material being worked which shall overcome the foregoing disadvantages of prior systems and which may be economically manufactured and installed. I8 A more speciiic object of my invention is to provide for maintaining a predetermined tension on translatory material over a wide variation in the position of the material from itsnormal path of movement.

Another object of my invention is to provide 5 for continuously increasing the tension on a strip of material as it passes through the roll stands of a rolling mill.

A further object of my invention is to maintain tension on material passing between work 10 devices by means of a device for applying a transverse deilecting force to the material and utilizing the movements of the forceapplying device for maintaining the length oi' the material between the work devices within predetermined 15 limits.

Other objects of my invention will be described fullyhereinafter or will be .apparent to those skilled in the art'.

In accordance with one embodiment of my 2o invention, which may b e applied to a rolling mill where it is desired to maintain a predetermined tension on the material between any two roll stands, the material is subjected to a transverse force at a point between the roll stands by means 25 tinuously increased as it passes through the rolls in order to compensate for the diierence in temperature between the head of the sheet and the end'of the sheet.

For a fuller understanding of the nature and objects of the invention, reference vmay be had 40 to the following detailed description taken in conjunction with the accompanying drawings, in which:

Figure 1 is a diagrammatic view ofv a portion of a rolling mill embodying my invention; 45

Fig. 2 is another diagrammatic view of the embodiment of the invention illustrated in Fig. 1;

Fig. 3 is a diagrammatic view of a modiilcation of the invention;

Fig. 4 is a diagrammatic view of another modi- 5o fication of the invention. and

Fig. 5 is' a view, in section, of a regulating valve utilized in the invention.

shown comprises roll stands III and II through which a strip of material I2, such as sheet steel, is passed. The roll stands I ,and II may be driven in any suitable manner, as by means of motors I3 and I4, respectively, which are connected to their respective roll members through gear sets-I5 and I6.

The roll motors I3 and I4 are provided with armature windings I1 and I8 and separately excited eld windings I8 and 28, respectively. The armature windings may be energized from any suitable source of direct-current power (not shown) through conductors 2| and 22, the motors I3 and I4 being connected thereto by controllers 23 and 24, respectively.` The eld windings I9 and 20 are energized from power conductors 25 antd 26, as will be explained more fully hereinaf er. I

In order to provide for maintaining a predetermined tension on the material I2, there is utilized a tensioning device for exerting a transverse deecting force on the material between the roll stands I0 and II. If a deilecting force is applied to the material |21 midway between the two stands so as to move it from the plane of the straight pass line `extending between the roll stands to a deected position, the tension on the material will be a function of the sine of the angle of deflection alpha and the tension will remain substantially constant so long as-the strip is maintained in this position under a constant force.

However, if the length of the material between roll stands increases and the same constant deiiecting force is applied, the angle of deection becomes greater and, therefore, the tension on the material is reduced. The opposite is true in the event that the length of the material between the roll stands decreases, thereby causing the tension on the material to increase.

In view of the' foregoing, it will be understood that in order to maintain a predetermined tension on the material, provision must be made for not only maintaining the tensioning means which applies the iorce to the material as nearly as possible in a certain position, but provision must also be made for causing a variation to occur in the amount of force produced by the tensioning means depending upon the degree of deflection of the material from its normal path of travel. In general, the pressure characteristic mustbesuch that the pressure increases with increasing height of the material abovethe pass line.

In the present invention, this result is accomplished by utilizing a tensioning device which comprises an idler roller 3i disposed to move up and down vertically in a pair of guides 32 between which the material I2 passes. The roller may be raised by a pair of duid-pressure operated pistons 33 disposed in cylinders 34, located underneath the idler roller crosshead 35. In order to maintain a predetermined tension for various positions o! the roll 3|, the pressure in the cylinders 34 is so regulated that the pressure increases as the roll is raised. It will be understood that the weight ofthe idler roller 3i and crosshead 35 may be counter-balanced by suitable weights or springs or other well knowndevices.

The ioregoing regulation may be accomplished by utilizing a regulating valve, shown generally at 38, to so vary the pressure ratio from inlet to outlet that with a constant inlet pressure a varying outlet pressure may be obtained. The outlet of the regulating valve 85 is connected to the cylinders 34 by means of a pipe 31 and the inlet of the valve may be connected to an air pressure tank (not shown) by means of a pipe 38. If desired, other suitable working mediums, such as any other gas or a liquid, may be utilized in place of air.

The construction of the regulating valve 36 is illustrated in detail in Fig. 5. The regulating valve comprises a body 4I provided with an inlet opening 42 and an outlet opening 43 whicn may 'be connected respectively to the supply line 38 and the line 31 leading to the iluid pressure operated pistons 33. The body 4I is provided with a spring cover 44 that houses a compression spring 45, the compression of which may be varied by means of a plunger 46. As shown, the spring 45 is disposed to control the position of a diaphragm 41 which-in turn, controls the operation of a valve 48. The compression of the spring 45 is adjusted in accordance with the pressure it is desired to maintain through the outlet opening 43. Air is admitted through the inlet opening 42 past the valve 48 until the pressure within the body 4I as applied to the diaphragm 41 is sufilcient to overcome the compressive force or the spring 45. The diaphragm 41 is thenv moved downwardly sufliciently to permit a spring 48 to close the valve 48, thereby preventing the further flow of air through the inlet opening 42. When the pressure within the body decreases to a value which is insufficient to maintain the diaphragm 41 in a position to permit the valve 48l to remain closed, the valve is opened slightly to permit air to ilow through the inlet opening to increase the pressure in the body of the valve and the outlet pipe 31. Thus, it will be seen that the outlet pressure may be regulated by varying thecompression of the spring 45. ,If the spring pressure is increased, the outlet pressure increases, and vice versa. s

The vertical movement of the roll 3| may be transmitted to the spring 45 in the pressure regulator in several different ways. As shown in Fig. l, a lever 5I, having one end connected to the roll crosshead at 52 and the other end disposed in a fulcrum 53, has an intermediate point sary to mount the valve 36 with the plunger 46- above the body member 4I, that is, upside down from the position-shown. xIHovveverqthis will=not affect the operation of the valve and the same results may be accomplished as with the arrangement shown in Fig. 1.

In the foregoing manner, a constant tension may be maintained on the material I2 for various positions of the roll 3I by so regulating the pressure on the pistons 33 that the pressure increases as the roll is raised. In someinstances, it is desirable to gradually increase the tension on a strip of material from the beginning of a pass to the end of the pass through the rolls I8 and II in order to compensate for the diil'erence in the temperature of the material. If it be assumed that a sheet of material is of uniform temperature when it enters the finishing mill of a hot strip mill and that the duration of one pass is from one to two minutes, it is apparent that the head of the strip leaves the last finishing stand' at a higher temperature than the end of the strip.

The difference in temperature may have a detrimental influence on the. gauge of the material which can be overcome by continuously increasing the .tension on the strip of material as it passes through the roll stands. This can be effected by so moving the fulcrum 53 -for the lever 5I that the compression oi the spring 45 -is continuously increased while the strip I2 is passing through the roll stands I0 and I I.

As shown in Fig. 1, the fulcrum 53 is slidably disposed on a base 56 and may be moved horizontally at a predetermined speed by a screw 51 driven by a motor 58, the operation of which may be controlled by a suitable controller 59 of a standard type. Power for operating the motor 58 may be supplied through conductors 6| and In this manner, the relative positions of the fulcrum 53 and the regulating valve 36 may be changed by operating the motor 58 at a speed to produce the desired change in tension while the material I2 is passing' through the roll stands,

thereby so changing the eii'ect of lthe vertical movement of the end 52 of the lever 5| on the spring that a continuously increasing tension is maintained on the material. It will be understood that the desired elect may be accomplished in other ways, as by utilizing another regulating valve unit which superimposes its pressure onto the working cylinders 34.

'I'he position of the fulcrum 53 may also be changed to permit the device to be set for drif-A ferent pressures depending upon the size of the sheet going through the mill. Thus, the largest sheets require the highest pressure in order to main-tain uniform tension on the material and the smallest sheets require the lowest pressure which may be readily adjusted by changing the position of the fulcrum 53.

As stated hereinbefore. air or any other -suitable gas or liquid may be utilized as the working medium -for actuating the ,pistons 33 in the cylinders 34. When air orga gas is utilized, it is desirable to provide a damper piston-63, in addition to the working pistons 33, to prevent bouncing of the cross-head 35.

As explained hereinbefore, the pressure regulator 36 and the idler roller 3| will maintain a predetermined tension on the material I2 over a wider range of operation than .previously known tensioning devices. However, better results will be' obtained if provision is made for maintaining the idler roller 3| In as neara predetermined operating position as possible. This may be accomplished by controlling the speed of at least one of the roll stand motors in accordance with the vertical movements of the tension roller 3|' dn such a manner that should the deilection of the material vary froma value considered as normal, the speed o! at least one of the motors is varied in order to take up the excess length in the strip of material or to increase its lengthas the case may be.

As illustrated in Fig. 2, provision is. made for automatically controlling the speed of the motor I3 by means of 'a regulator device 64, the functloning of which is c'aused to be linfluenced in accordance with the position of the roller 3|. As stated hereinbefore, the separately excited eld windings I9 and 20 `of the motors I3 and I4, respectively, areenergized from the power conductors 25 and 26. The field circuit of the motor I4 is provided with a variable resistance 65 which may be utilized to adjust the speed of the roll stand II. Likewise, the motor I3is provided with, a field rheostat 66 which may be utilized to adjust the speed of the roll stand I0. In addi.

power conductors 25 and 26 are energized, the

electromagnet 13 is energized and raises the contact element 12 to its uppermostposition. The energizing circult for the electromagnet 13 contains a resistor 15 which is shunted by the auxiliary relay 14. Upon the operation vof the 4electromagnet 13, its contact members 16 are closed to energize the auxiliary relay 14 which opens its contact' members to insert' the resistor 15 in the circuitfr the electromagnet 13. This increases the resistance of the circuit of the electromagnet 13 to such an extent that thevibrating contact element 12 is returned to its lowermost position. This cycle of' operation is repeated, thereby causing the contact element 12 to vibrate.

The regulator is provided with an adjustable contact element 11 having upper and lower contacts which are positioned in any suitable manner in accordance with the position of the roller 3|. As shown, the contact element 11 is connected to the roller cross-head 35 by means of a lever mechanism 18. However, it will be under,- stood that the movement of the roller 3| may be transmitted tothe contact element 11 in any other suitable manner.

In order to morev clearly describe the functioning ofthe regulator 64 to control the speed of the motor I3 in accordance with the movements of the roller 3|, it will be assumed that the material I2 is traveling in the direction indicated by the arrow. Under Ithis condition, the speed of the motor I3 must be increased when the deilection increases, and decreased when the deflection decreases. f

When the vibrating contact element 12 is in its lower position, it engages the lower contact of the adjustable contact element 11, and the shunting switch 1I is energized to remove the shunt connection from the ileld resistor 66, thereby decreasing the excitation of the motor I3 and increasing its speed accordingly. When the contact element 12 is in itsV upper position, the shunting switch 69 is energized to shunt the resstor 61 from the field circuit, ,thereby increasing the excitation of the motor, which causes its speed to decrease.

The regulator 64 is so disposed that when the tension roller 3| is in its normal operating position, the vibrating contact element 12 makes contact with the upper and lower contacts ofthe adjustable contact .element 11 for equal periods' it engages the upper contact, thereby causing the shunting switch 1I to be maintained in its open position over longer periods of time than the shunting switch 88, which causes the speed of the motor I3 to increase a suflicient amount to reduce the deiiection of the material |2 to normal. A

The opposite is true when the deiiection decreases below its normal value, thereby causing the shunting switch 59 to be maintained energized over longer periods of time than the switch In this manner, the speed of the motor I3 is decreased, and the deflection of the material I2 increased.

As an alternative to the mechanical connection between the idler roller 3| and the pressure regulating valve 36, hereinbefore described, an electrical connection may be utilized, if desired. As shown in Fig. 3, the pressure regulator 38 is of the same type as previously described. However, the spring 45 is normally compressed to an amount that will cause the maximum pressure to be maintained in the operating cylinders 34 which may at any time be required. The spring pressure is counteracted by the pull oi a solenoid magnet 8|, which is connected to the plunger 46 to reduce the pressure of the spring 45 on the diaphragm 4l, thereby relieving the diaphragm of part of the pressure exerted on it by the spring 45. The force produced bythe solenoid magnet 8| is so regulated that with the roller 3| in its lowest position the magnet 8| exerts its maximum force, practically balancing,

the force of the spring 45. As the roller 3| moves up, the current in the solenoid 8| is decreased a suitable amount to permit the spring pressure on the diaphragm to be increased. In this man ner, a definite spring pressure is exerted on the diaphragm for each position of the roller, thereby producing a definite pressure on the pistons 33 which support the roller 3|.

As shown in Fig. 3, the current in the coil 82 of the solenoid 8| may be controlled in accordance with the position of the roller 3| by means of a lever operated rheostat 83. The rheostat 83 is connected'in series with the coil 82 which may be energized from power conductors 84 and 85. The lever arm 86 of the rheostat`83 may be connected to an extension 81 on the cross-head 35 by a link 88 to transmit the motion of the crosshead to -the arm 88, thereby controlling the current in the solenoid coil 82.

In order to provide an adjustment for a variation in the size of the sheets of material being rolled, which requires a variation in the pressures necessary to maintain a constant tension in the material, as explained hereinbefore, a manually adjustable rheostat 9| may also be connected in the circuit for the coil 82 of the solenoid 8|. In this manner, the current in the solenoid 8| may' be so adjusted that it exerts a maximum force for the largest size of sheets, and a minimum force for the smallest size which are to be rolled through the roll stands I8 and I In the modiiication of the invention `shown in Fig. 4, the variable rheostat 83 is utilized to control the iield excitation of a generator 82, which, in turn, energizes the coil 82 oi' the solenoid 8|. The generator 92 may be driven by a motor 83 which may be connected to power conductors 94 by means of a switch 85. It will be understood that as the roller 3| is raised, the current in the iield winding 88 of the generator 92 is decreased, thereby lowering the voltage of the generator 92 and decreasing the current in the coil 82, which decreases the pull exerted by the solenoid magnetand permits the spring 45 to increase the aaanssa pressure on the diaphragm of the regulating valve 38, thereby increasing the iiuid pressure on the pistons 33 which actuate the roller 3| to maintain a predetermined tension on the material I2. As explained hereinbefore, a manually adjustable rheostat 8| may be connected in the circuit for the solenoid coil 82 to adjust the tension for different sizes of sheets of the material I2.'

From the -foregoing description, it is apparent that I have provided a tension regulating system which will operate satisfactorily over a wide range of movement of the tension roller. Furthermore, the system may be readily adjusted for various classes and sizes of material, and, if desired, provision may be made for continuously increasing the tension on `the material to compensate for changes in the temperature of the material while it is being worked, in the manner hereinbefore described.

Since numerous changes may be made in the i above described construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all matter .contained in the foregoing description, or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In a tension control system, in combination, a movable .tensioning roller, duid-pressure means for actuating said roller, and means responsive to the movement of said roller for controlling the operating pressure of the fluid-pressure means.

2. In a tension control system, in combination. a movable tensioning roller, iiuid-pressure loperated means for actuating said roller, and means responsive to the movement of said roller for regulating the pressure applied to the fluidpressure operated means, thereby controlling the operation of said tensioning roller.

3. In atension Vcontrol system, in combination, a movable tensioning roller, duid-pressure operated means for actuating said roller, and valve means controlled by the movement of said roller for regulating the pressure applied to the fluid-pressure operated means, thereby controlling the operation of said tensioning roller.

4. In a system for controlling the tension on a length of materiaLin combination, a movable tensioning roller, iluid-pressure operated means for actuating said roller into engagement with said material, and valve means actuated by the movement of said roller to vary the pressure aD- plied to the fluid-pressure operated means, thereby controlling the tension Aon said material. v 5. In a system for controlling the tension on a length of material extending between two points, in combination, a movable tensioning member, uid-pressure operated means for so actuating said movable tensioning member as'to cause the member to deect the lengthof material from the line between the'two points to thus subject the length of material to tensiomand means responsive to the movement'of said tensioning member for varying the pressure appliedto the fluid-pressure operated means in wccordance with the degree of movement of'said member, thereby controlling the tension on thev material. 6.- In a system for controlling the tension on a length of material as it extends between two points, in combination, a movable tensioning member, fluid-pressure operated means for so actuating said tensioning member as to cause the member to deect the length of material from the line between the 4two points to thus subject the length-of material to tension, and uuid-pressure regulating means actuated by the movement of said tensioning member for varying the pressure applied to the fluid-pressure operated means in proportion to the degree of movement of said member, thereby regulating the tension on the length of material.

7. In a system for controlling the tension on a length of material as it extends between two points, in combination, a movable tensioning member, duid-pressure operated means for so actuating said tensioning member as to `cause the member to deflect the length of material from the line between the two points to thus subject the length of material to tension, and iiuidpressure regulating means actuated by the movement-of said tensioning member for increasing the pressure applied to the fluid-pressure oper- .ated means in direct proportion to the degree of movement of the member, thereby maintaining a predetermined tension material.

8. In a system for controlling the tension on a strip of material, in combination, a pair of roll stands for rolling the material, an idler roller disposed between said roll stands, fluid-pressure operated means for actuating said roller to apply pressure on the material to create a tension therein, uid-pressu-re regulating means for regulating the pressure in said fluid-pressure operated means, and means responsive to the movement of said roller for adjusting said regulating means to varythe pressure in said fluid-pressure operated means, thereby maintaining a predetermined tensiony on said material.

9. In a system for controlling the tension on a strip of material, in combination, a pair of roll on the. length of stands for rolling the material, an idler roller .15 regulating the pressure in said uuid-pressure op- G0 pressure on said piston, meansfor transmitting erated means, and means responsive to themovement of said roller for adjusting said regulating means to vary the pressure in said fluid-pressure operated means in proportion to the movement of said roller, thereby maintaining a predetermined tension on said material.

1G. In a system for controlling the tension on a strip of material, in combination, a' pair oi' roll stands f0.1` rolling'the material, means for driving each of said roll stands, a tension roller disposed between said roll stands, a fluid-pressure operated piston for moving said roller vertically Ato apply a transverse pressure onsaid material, aregulating valve for regulating the the vertical movement of said roller to said regulating valve to adjust the setting thereof, thereby varying the pressure on said piston in accordance with the position of said roller, and regulating means responsive to the vertical movement of said roller for governing the speed of the driving means for -one of said roll stands.

l1. In a system for controlling the tension on a strip of material, in combination, a pair of roll stands for rolling the material, a tension roller ldisposed between said roll stands, a iiuidpressure operated piston for moving lsaid roller vertically to apply a transverse pressure on said material, a regulating valve for regulating the 75 pressure on said piston, and a lever for adjusting said regulating valve in accordance with vthe position of said roller, thereby varying the .pressure on said piston in proportion to the `movement of the roller to control the tension on said material.

12. 1n a system for controlling the tension 4on a strip ofmatenal, in combination, a pair of roll stands for rolling the material, a tension roller ydisposed between said roll stands, a fiuidpressure operated piston for moving said roller vertically to apply a transverse pressure on said material, a regulating valve for regulating the pressure on said piston, a lever for adjusting said regulating valve in proportion to the movement of said roller to vary the pressure on said piston, and means for changing the eiect produced by said lever on said regulating valve.

13. In a system for controlling the tension on a strip of material, in combination, a pair of roll stands for rolling the material, a tension roller disposed between said roll stands, a fluidpressure operated piston for moving said rollervertically to apply a transverse pressure on said material, a regulating valve for regulating the pressure on said piston, a lever for adjusting the setting of said regulating valve in accordance with the position of said roller to vary the pressure on said piston, and means for varying the eiective length oi' said lever thereby changing the setting of said valve to vary-the pressure `exerted by said roller on said material.

14. In a system for controlling th tension on a strip of material, in combination, a pair of roll stands for rolling thematerial, a tension a strip of material, in combination, a pair of` roll stands for rolling the material, a tension roller disposed between said roll stands, a fiuid` pressure operated pistoni'or moving said roller vertically to apply a transverse pressure on said material, a regulating valve for regulating the ypressure on said piston, av lever for adjusting ing means for controlling the pressure applied Ato said Enid-,pressure operated means,'electri cally-energized means Vfor, adjusting said regulating means, and means for chang'ing'theeffect of said electrically-energized means in accordance with the position of said roller, thereby controlling the tension on said material.

, 17. In a system for controlling the tension on a length of material, in combination, a vertically movable tensioning roller, uid-pressur operated means for actuating said roller, a regulating means for controlling the pressurefapf plied to said duid-pressure operated means, electrically-energized means for adjusting said regulating means, and means actuated by the movement of said roller for controlling the energization of said electrically-energized means in accordance with the position of said roller.

18. In a system for controlling the tension on a length of material, in combination, a vertically movable tensioning roller, duid-pressure operated means for actuating said roller, regulating means for controlling the pressure applied to said fluid-pressure operated means, electricallyenergized means for adjusting said regulating means. means actuated by the movement of said roller for controlling the energization of said electrically-energid means in accordance with the position of said roller, and additional means for controlling the energization of said electrically-energized means to vary the tension on said material.

19. In a system for controlling the tension on a length of material, in combination, a vertlcally movable tensioning roller, fluid-pressure operated means for actuating said roller, regulating means for controlling the pressure applied to said duid-pressure operated means, electrically-energized means for adjusting said regulating means, a generator for energizing said electrically-energized means, and means tor varying the potential 'oi' said generator in accordance with the position of said roller.

20. In alsystem for controlling the tension on a length oi material, in combination, a vertically means, a generator for energizing said electril cally-energized means, means for varying the potential of said generator in accordance with the position of said roller, and adjustable means for controlling the current in said'electricallyenergized means, thereby controlling the tension on said material. Y

21. In a system for controlling the tension on a length of material, in combination, a vertically movabletensioning roller, iiuid pressure operated means for actuating said roller, a uid pressure regulating reducing valve for controlling the pressure applied to said iluid pressure operated means, said regulating valve having an inlet opening and an outlet opening and comprising a diaphragm positioned to be displaced by the regulated iiuid pressure, means whereby displacement of said diaphragm Aby the regulated iiuid pressure tends to close the valve, means biasing said diaphragm in the direction of diaphragm movement which will open the valve. electromagnetic means acting in opposition to said biasing means, and means for controlling the energization of said electromagnetic means in accordance with the displacement of said roller by said iluid pressure operated means.

GERHARD P 

